Arm200cf

The atomic structures of the SrCoO_2.5−σ films was characterized using an ARM—200CF (JEOL, Tokyo, Japan) transmission electron microscope operated at 200 kV and equipped with double spherical aberration (Cs) correctors. The attainable resolution of the probe defined by the objective pre-field is 78 picometers. ABF and HAADF images were acquired at acceptance angles of 11–22 and 90–250 mrad, respectively. All of the images presented here are Fourier-filtered to minimize the effect of the contrast noise. The filtering does not have any effect on the results of our measurements. In addition, we adjusted deliberately the brightness and contrast in order to better representation of the atomic arrangements, this adjustment does not have any effect on the result. The EELS experiments were carried out with a Gatan spectrometer attached to the TEM in the STEM mode operating at 200 kV. The convergence semi-angle for the electron probe was 22 mrad. The spectrometer was set to an energy dispersion of 0.25 eV/channel. All of the spectra were acquired with a short exposure time, which was as short as 0.05 s, in a line-scan manner. Three hundred spectra were summed to avoid electron beam damage.

High‐resolution XRD measurements were performed using a Rigaku Smartlab and a PANalytical X'Pert XRD. Atomic‐scale imaging of SLs was performed on a spherical aberration‐corrected scanning transmission electron microscope (STEM; ARM200CF, JEOL) operating at 200 kV. To detect the β‐dependency of octahedral distortions in SRO layers, the annular bright‐field (ABF) imaging mode was employed along with the high‐angle annular dark‐field (HAADF) imaging mode. The incident electron probe angle was set to 23 mrad, giving rise to a probe size of 0.78 Å. The ABF and HAADF signals were simultaneously collected over detector angle ranges of 7.5–17 and 70–175 mrad, respectively. Cross‐sectional thin samples for STEM analysis were prepared using a dual‐beam focused ion beam system (FIB, FEI Helios Nano Lab 450); subsequently, low‐energy Ar ion milling at 700 V (Fischione Model 1040, Nanomill) was carried out for 15 min to remove surface layers damaged owing to heavy Ga ion beam milling in the FIB system.

X-ray diffraction (XRD) patterns were measured by a Shimadzu LabX XRD-6000 diffractometer with Cu kα radiation (λ = 0.15406 nm). Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analyses were performed on a Hitachi S-4800 microscope and an FEI-Tecnai G² 20 microscope, respectively. XPS measurements were conducted by using a VG ESCALAB 250 instrument with a monochromatized Al X-ray source (1486.6 eV). Nitrogen adsorption–desorption isotherms were obtained from a Quadrasorb instrument at 77 K. ICP-AES was detected by a Perinlmer Optima 2000DV instrument. The HAADF-STEM images were obtained on a JEOL ARM200CF fifth order aberration-corrected TEM equipped with a dual-type EDS detector. The X-ray absorption find structure spectra were measured at the BL8C beamline in Pohang Light Source (PLS), Korea.

Transmission electron microscopy (TEM) was
performed on a JEOL JEM-2100 operating at 200 kV. Energy dispersive
X-ray analysis (EDX) was done using an Oxford Instruments X-MaxN 80
detector, and the data were analyzed using the Aztec software. Samples
were prepared by dispersion in ethanol by sonication and deposited
on 300-mesh copper grids coated with a holey carbon film. High angle
annular dark-field (HAADF) scanning transmission electron microscopy
(STEM) imaging was done using a JEOL ARM200CF operating at 200 kV.